Gamete cell surface components confer specificity in events critical for processes of reproduction and development. Antibodies can block gamete function and embryogenesis, but the specific molecules involved have not been identified. Monoclonal antibodies are being produced to characterize these molecules, determine their origin and distribution, and define their roles. There are three aspects of the project. (a) One study has examined the appearance of new sperm surface components during epididymal maturation, coincident with sperm gaining the ability to swim and to fertilize. A 54,000 molecular weight antigen being studied is secreted by epithelial cells in the caput epididymidis and attaches specifically to acceptor sites on the plasma membrane of the flagellum. It is cell type and species specific, present in the epithelium after two weeks of age, absent from sperm recovered from the oviduct, lost during in vitro capacitation, but retained on sperm incubated in the presence of mouse or rat epididymal fluid. (b) An additional study has examined sperm surface components that may be involved in the acrosome reaction. Surface molecules are lost during the acrosome reaction as shown by using a monoclonal antibody to monitor antigen loss and a protease activity assay to measure calcium-stimulated acrosomal enzyme release. The protease release was inhibited in sperm exposed to antibody prior to calcium treatment. (c) Another study has examined surface antigens shared by germ cells, teratocarcinoma cells, and embryonic cells. Some of these are high molecular weight glycoproteins and stage-specific expression of particular antigens during spermatogenesis is due to changes in patterns of sialic acid incorporation during post-translational modification of glycoconjugate.